The present invention relates to a color decoder for a color television receiver of the type in which the color signals obtained in demodulators from the modulated chrominance subcarrier are obtained with a delay of one picture line period in delay lines designed as charge transfer circuits and the color difference signals are obtained from the delayed and the undelayed signals in adder stages which act as a matrix, the delay lines, the demodulators and the adder stages being constructed as integrated circuits on a semiconductor chip.
In order to demodulate the PAL chrominance subcarrier it is known to delay the chrominance subcarrier by one picture line period in a glass ultrasound delay line and to add, to the delayed chrominance subcarrier in successive adder stages, the undelayed chrominance subcarrier and the undelayed chrominance subcarrier which has been shifted in phase by 180.degree., respectively. This produces a split of the signal into the two carrier frequency components (R-Y) and (B-Y). The (B-Y) component is demodulated in a first demodulator with the use of a reference carrier generated by a reference carrier oscillator and the (R-Y) component, whose phase alternates from line to line by 180.degree., is demodulated in a second demodulator with the use of a reference carrier which has been shifted by 90.degree. and is switched by 180.degree. from line to line. In this way the two video frequency color difference signals (B-Y)' and and (R-Y)' are produced which constitute an average over two lines. This manner of decoding has the drawback that a glass delay line is required which cannot be integrated in modern semiconductor circuits.
The periodical Funk-Technik, 1971, No. 6, at pages 195-198, discloses the use of two bucket brigade circuits in the PAL decoder instead of a glass delay line. Since the bucket brigade circuits have the characteristic of a lowpass filter, they can be used only to delay video frequency signals. For that reason, the known decoder splits the chrominance subcarrier by means of two synchronous demodulators into the two video frequency signals (B-Y) and (R-Y). These signals are then delayed by one picture line period in a delay line designed as a shift register for analog signals. By adding the two undelayed signals to the correponding delayed signals, the two color difference signals (B-Y)' and (R-Y)' are generated in an adder stage. Thereafter the two color difference signals (B-Y)' and (R-Y)' are fed, in a given ratio, to a further adder stage serving as matrix which generates the color difference signal (G-Y)' therefrom. This decoder has the drawback that it requires a large number of structural components.